Variation in total and specific RNA during inwintering of two contrasting populations of Picea abies

Seedlings of a southern (Romanian) and a northern (Swedish) population of Picea abies (L.) Karst. were cultivated in a phytotron under continuous lighl and 20°C for 10 weeks. Subsequently they were exposed to a regime of long nights (16 h). initially at 20°C but with stepwise lowering to 10°C over 12 weeks. Samples of needles were taken for total RNA extraction and studies of gene expression at intervals from just before the change of regime and onwards. At the same time samples were taken for abseisic acid (ABA) determination. Extension growth, degree of budrest and frosl tolerance were also recorded. The main results were as follows. (1) Extractable total RNA per g fresh weight of needles increased by 150–250% through the period of long nights. (2) The capacity of the total RNA to direct protein synthesis in a cell-free system declined in response to long nights to a minimum value of 5% (northern population) and 23% (southern population) of the reference values under continuous light. (3) In vitro translatability was highly correlated with the size of the polyadenylated fraction of the total RNA, which declined also when normalized to needle fresh weight rather than total RNA. (4) A peak of abscisic acid content in the southern population at 3 days into the long night treatment coincided with a trough in the in vitro translatability of the total RNA. (5) The steady state levels of rbc S-mRNA as a fraction of total RNA declined rapidly to a final value of about 15% of the reference value in both populations, the decline being more rapid for the northern population. (6) In contrast. ubiquitin-mRNA showed an initial increase, particularly in the northern population, and at the end of the long night treatment was only 40% under the reference value. (7) Rapid changes in the molecular characters occurred during the first 3–4 weeks when the morphological and physiological changes were most rapid.